Runoff water flowing off buildings, gutters and downspouts carries with it numerous chemicals, suspended solids and other pollutants that are undesirable in ground water, streams and rivers. As such, it is important to remove such pollutants from the runoff water. One notorious example of a pollutant often found in runoff water is zinc. Metal buildings typically use a significant amount of zinc. As rainwater runs over the surface of metal buildings, zinc is picked up by and carried in the water—generally the runoff water is slightly acidic and the zinc thus is solubilized in the water. Corrosion and runoff from zinc-coated materials used in buildings and other sources such as tires, heavy equipment, chain link fencing and treated wood is a large source of zinc pollution in the environment. Depending upon the type of drainage system around metal buildings, the runoff water and all of the pollutants, and notoriously zinc, it carries eventually finds its way into municipal sewer treatment systems, and then into rivers and streams. However, zinc and many other compounds carried in the runoff water are often not removed from the water, and therefore enter the environment where they pose significant pollution problems. In addition to the example of zinc just mentioned, water running off metal buildings and other structures picks up a wide variety of other pollutants, ranging from large and small debris, suspended solids and sediment to oils and other soluble and insoluble chemical contaminants.
Ideally, all runoff water would be routed into a variety of filtering systems to remove pollutants, whether the filtering systems are found in a municipal storm sewer system or some other less formal surface water filtering system. In a municipal type of system a series of grated catch basins or other collection boxes are interconnected with sewer pipe. Surface water flows through the grate, dry wells, swales and retention ponds, which catch large objects such as branches, rocks and the like. The water that flows through these primary filters enters the catch basin, which is a collection box or vault that functions essentially a settling basin. Such collection boxes are sometimes called sump tanks. Some sediment that flows through the grate settles to the bottom of the basin, and the water flows through an outlet pipe and into the sewer system and, depending upon the system, either to another processing facility or directly into a stream or river.
This traditional system is useful as a primary control system, and is relatively inexpensive, but it has many problems. As an initial consideration, it would be preferable to remove as much pollution from the water before it reaches a collection box. As examples of other problems, the catch basin can quickly be filled with sediment if the water contains a high level of solids or sediment, causing the catch basin to become filled and the system to overflow or become clogged. Because the catch basin is typically a cylindrical tube or a rectangular box that sits below grade level, cleaning the sediment out of the basin can be a difficult job. Cleaning is made much more difficult if the system is clogged and the basin is underwater. Just as important, the system does not stop all of the sediment and other pollutants in the run-off. Typically, the water flow through the basin is fairly turbulent, especially when there is a lot of water flowing through the system, for instance during a storm. When this occurs very little sediment settles out, and is instead washed through the basin and into the sewer system. This may result in non-compliance with governmental regulations, possibly resulting in fines. Finally, a typical catch basin system does nothing to collect oils and other chemical contaminants and dissolved solids. This is especially true in the case of water running off of metal buildings: traditional catch basins do not remove hazardous materials such as zinc.
Many government agencies monitor contaminants that are carried into streams and rivers in runoff water, both in municipal and private systems. Many municipalities impose fees and fines on property owners based on the nature and quantity of contaminants contained in water escaping from the property. While these fees apply in most instances to commercial users, they can also apply to residential systems. In large part the fees are based in some manner on the kind and amount of pollutants that flow through the catch basin and into the system. In general, the higher the level of contaminants flowing through the system, the higher the fee. In some cases the amount of the fee is based on the kind of contaminant. For example, oils flowing into a sewer or dry well can lead to increased fees. These fees even apply to private commercial dry well users, since it is in the interest of a municipality to control the amount of pollution that enters the ground water. Zinc is one of the primary pollutants that municipalities routinely test for in runoff water, and phosphorous and various heavy metals are also pollutants of keen interest for removal.
In addition to environmental reasons for reducing the amount and kind of contaminants in runoff water, given the possibility of fines being levied or even the potential for lawsuits, there is therefore a strong incentive for property owners to decrease both the amount and kind of contaminants flowing off property and into either a municipal sewer system or a private dry well or sewer system. First, there is an obvious environmental incentive: by decreasing contamination of all kinds from surface water runoff, the water that flows back into the ground and into streams and rivers is cleaner. This helps to improve environmental conditions in numerous ways. Second, there is a strong economic incentive: when sewer system and dry well users are paying fees based on the amount and kind of contaminants that flow into their systems, it is of obvious advantage to minimize all contaminants.
Given the need to effectively filter debris and contaminants from surface water run-off, various catch basin and other filter systems have been devise. As one example, U.S. Pat. No. 5,284,580 describes a collecting frame for use with a drainage sewer. The system utilizes a basin that fits into the sewer drain and is removable therefrom. The basin has a filtering net for trapping debris that flows into the basin through a sewer cover. An imperforate collecting basin catches particulate matter while tiny particles flow through the system with the run-off water. While this device filters out some particulate matter, it does not stop small particles, oils or chemical pollutants from entering the sewer system.
Another example of a surface water filter system is disclosed in U.S. Pat. No. 5,405,539. The system disclosed in the '539 patent is inserted into an existing storm drain collection box. A frame supports a runoff of filter medium, such as a woven synthetic material that removes particles as small as 42 microns in diameter. Pneumatic rams hold the filter material and frame in place in the collection box. Silt and other particulate debris collects on the filter compartment until the woven filter is clogged and/or the filter compartment is full, at which time excess drainage water overflows, unfiltered, over the back of the filter drain and into the sewer system. The woven filter is replaced by removing the spent runoff from the collection box and replacing it with fresh material.
Yet another filter system is disclosed in U.S. Pat. No. 5,372,714. This system is adapted for use with buried, below grade catch basins, and utilizes a filter bag made of a woven plastic fabric that is porous, but which captures solids. The filter bag hangs into the catch basin, supported by the overlying grate. When full, the bag is removed by inserting lifting rods into loops of fabric connected to the bag.
And U.S. Pat. No. 6,200,484 describes a filter system that utilizes a sump tank insert that is sized to fit into an existing catch basin. Runoff flowing into the system goes through three filters. The first is the traditional grate that overlies the inlet to the catch basin, which catches large solid particles such as rocks and branches. A secondary filter is a perforate screen that traps solids that flow past the grate. The water flows through the screen into a collecting vault where even smaller solids that flow through the screen settle out. A third filter is a filter media through which all water flows, and which is held in a removable frame. The filter media selected for this tertiary filter depends upon the conditions encountered at a specific location, and may be specific to absorb oils and petrochemicals, as might be expected in runoff from parking lots. Similarly, oils are often contained in runoff from food processing facilities. Another kind of filter media that can be used is media specifically designed for filtering out carbohydrates. This type of media is used with, for example, catch basins that collect water that has been used as process water in food processing facilities.
Despite these and other solutions for filtering surface runoff water, there is a strong need for simple, economical and efficient filtering systems and apparatus for removing contaminants from runoff water, and there is a particular need for improved apparatus for removing pollutants from surface runoff before the water flows into a catch basin such as those described above.
The runoff water filter of the present invention is designed to be used without any other ancillary components; the filters may be placed directly into the effluent or runoff stream so that pollutants are removed from the runoff prior to the water entering a municipal collection system. The filter is defined by a container that is readily permeable to water and a filter medium that is contained within the container. The type of filter media selected depends upon the requirements for the particular location, but in the preferred embodiment is defined by media capable of removing zinc from the runoff water.